Bis(tetrahydrofuroyl) peroxides



"pressures, for example, 10,000 p.s.i. or higher.

United States Patent 3,206,481 BIS(TETRAHYDROFUROYDPERGXEDEQS James E.Gnillet and Edmund B. Towne, Kingsport,

TemL, assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey No Drawing. Filed July 27, 1061, Ser- No. 127,106 5Ciaims. (Cl. 260-447.?!)

This invention relates to the polymerization of ethylenicallyunsaturated polymerizable compounds and particularly to novel catalystsuseful for this purpose. In a specific aspect, this invention relates tonovel diacyl peroxides and their use as catalysts in the polymerizationof ethylenically unsaturated polymerizable compounds. In a more specificaspect, this invention concerns the preparation of polyethylene having ahigh density, i.e. polyethylene having a density of at least 0.94, inthe presence of a novel diacyl peroxide.

It is known that ethylenically unsaturated compounds, and particularlyethylene, can be polymerized at temperatures in the range of about 40 toabout 400 C. at high Catalysts that have been suggested for use in thesehigh pressure processes include oxygen, per-salts, diacyl peroxides,metal alkyls and 220 compounds. However, but for a few noteworthyexceptions, the diacyl peroxides that are employed as catalysts in themany varied high pressure polymerization reactions are deficient aswholly desirable polymerization catalysts at lower temperatures, forexample, 150 C. or lower.

The density of a polymer, and particularly polyethylene, prepared in ahigh pressure process is particularly dependout upon the temperature ofthe polymerization. At lower temperatures higher density polyethylene,e.g. polyethylene having a density of at least 0.94, is obtained, whileat higher temperatures a lower density polyethylene, e.g. polyethylenehaving a density less than 0.935, is obtained. Polyethylene having adensity of at least 0.94 is particularly valuable due to its improvedphysical properties including, for example, increased mechanicalstiffness which allows the preparation of articles having greaterrigidity than those obtained with lower density polyethylene.

The temperatures necessary to prepare polyethylene having a density ofat least 0.94 in the high pressure processes are about 150 C. or below,and more usually below about 100 C. In order to prepare such polymers ina high pressure process, it is, therefore, necessary that the catalystdecompose very rapidly at temperatures below about 150 C., or morepreferably at temperatures below 100 C., to initiate the polymerizationreaction. Diacyl peroxides such as lauroyl, butyryl, acetyl and benzoylperoxides have been used in the high pressure polymerization ofpolyethylene. Although such peroxides are effective in batchpolymerizations where reaction times in the order of several hours to 24hours are used, "they cannot be used in continuous reactors attemperatures below about 150 C. because, at these lower temperatures,the rate of production of free radicals is not rapid enough to sustainthe polymerization reaction. For example, lauroyl peroxide is effectivein polymerizing ethylene in batch reactions at temperatures of 100 C.and higher, but, at temperatures below 100 C., excessively long timesare required for the polymerization reaction and the yields ofpolyethylene are very low. Alternatively, in a continuous polymerizationprocess, the minimum opcrating temperature for lauroyl peroxide is about170 C.

It is evident, from the discussion set forth above, that the state ofthe art will be greatly enhanced by providing a class of diacyl peroxidecatalysts which reach their maximum eificiency at temperatures of about150 C. or lower, and more preferably at temperatures of 100 C. or

Patented Sept. 14-, 1965 below. Likewise, a noteworthy contribution tothe art will be a method for the polymerization of ethylemcallyunsaturated compounds employing such catalysts at temperatures of 150 C.or lower.

Accordingly, it is an object of this invention to provide novel diacylperoxide catalysts that are effective to polymerize ethylenicallyunsaturated polymerizable compounds.

Another object of this invention is to provide diacyl peroxide catalyststhat are effective to polymerize ethylenically unsaturated compounds attemperatures of 150 C. or below, and more preferably at temperatures ofC. or below.

A further object of this invention is to provide a catalyst that isparticularly effective in the preparation of higher densitypolyethylene, i.e. polyethylene having a density of at least 0.94.

Other objects will become apparent upon an examination and considerationof the specification and claims which follow.

In accordance with this invention it has been found that ethylenicallyunsaturated polymerizable compounds, and particularly ethylene, can bepolymerized at temperatures Within the range of about 30C. to about C.,in the presence of novel diacyl peroxide catalysts, as hereinafterdescribed.

The novel diacyl peroxide catalysts of this invention possess thegeneral formula:

( rt J used in the specification and claims indicates a tetrahydrofuroylring which is, of course, devoid of aromatic unsaturation.

it was completely unexpected that diacyl peroxides having the aboveformula could be used at low temperatures in the high pressurepolymerization of ethylenically unsaturated polymerizable compoundssince corresponding unsaturated peroxides, e.g. bisfuroyl peroxide, arenot low temperature catalysts in the high pressure polymerization ofethylenically unsaturated polymerizable compounds but must be used atelevated temperatures in order to obtain practical yields of polymer.

The R group, as indicated above, can be any alkyl radical and desirablycontains 1 to 12, and more preferably 1 to 4 carbon atoms. Suitable Rgroups, therefore, include methyl, ethyl, propyl, isopropyl, butyl,tert.-butyl, decyl, dodecyl, tetradecyl and the like. Hence, examples ofthe novel diacyl peroxides included within the scope of this inventionare tetrahydrofuroyl peroxide, bis (S-methyltetrahyclro-Z-furoyl)peroxide, bis(4-methyl tetrahydro-2-ruroyDperoxide, bis(5-tert.-butyl tetrahydro 2 furoyl) peroxide and thelike.

In order to obtain maximum catalyst efiiciency, a peroxide catalyst mustdecompose completely during the reaction but not so rapidly as todecompose in the first few seconds. In discussing the rate ofdecomposition of peroxides, it is convenient to use a measurement of thehalf-life T. This is defined as the time required at any giventemperature for /2 of the peroxide to decompose. In dilute solution inan inert solvent, most peroxides show a unimolecular decomposition inwhich the half-life is constant, independent of the initialconcentration and of the solvent, and dependent only on temperature. Thehalf-life of the peroxide can be determined in a number of ways. Aconvenient method is to heat a dilute solution of the catalyst in asolvent such as heptane or toluene for a given length of time at aconstant temperature. The unexpectedly rapid rate of decomposition ofthe novel diacyl peroxides of this invention at low temperature isillustrated by the following table setting forth the half-life 'r at 70C. in toluene solution at a concentration of 1% of tetrahydrofuroylperoxide and some conventional prior art peroxide catalysts.

Table 1 Half-life at Compound: 70 0., min. Acetyl peroxide 725 n-Butyrylperoxide 425 Lauroyl peroxide a 438 Furoyl peroxide 437Bis(tetrahydrofuroyl)peroxide 38.3

It is the rapid rate of decomposition on the novel diacyl peroxides ofthis invention at low temperatures which makes them eminently suitablefor use as low temperature polymerization catalysts.

A convenient method for preparing the novel peroxides of this inventioncomprises reacting an acyl halide of the formula:

where R and n are as defined hereinbefore, and X is halogen, forexample, chlorine or bromine, with an inorganic peroxide such as analkali. or alkaline earth metal peroxide, for example, sodium, calciumor barium peroxide at a relatively low temperature in the range of about-40 C to +15 C., and more preferably in the range of about 0 C. to about+5 C. While the reaction mixture can be allowed to rise to temperaturesup to about C., for example, as a precautionary measure, temperatures inexcess of 25 C. are to be avoided. In; a preferred mode of preparingthese peroxides a toluene solution of the halide is added gradually as,for example, dropwise at a temperature in the range hereinbefo'redisclosed, to a toluene solution of the alkali or alkaline earth metalperoxide. The reaction is continued to completion which is usually aperiod of not more than 7 hours after mixing the reactants. Theresulting peroxide can then be isolated by conventional isolationprocedures. Although not essential, it is usually desirable to use aslight excess of inorganic peroxide.

Other reaction media besides toluene, for example, any aliphatic,cycloaliphatic or aromatic hydrocarbon, or their mixtures, can beemployed. Best results are, in general, obtained with toluene alone. Theamount of toluene employed is subject to wide variation. Twenty to onehundred parts of toluene per part of sodium peroxide, for example,usually give satisfactory results. Furthermore, any of the conventionalaliphatic, cycloaliphatic, or aromatic solvents can be used as thesolvent for the halide reactant. Suitable solvents for this purposeinclude, for example, benzene, toluene, heptane and the like.

The temperatures employed in the polymerization reaction are subject towide variation and depend upon such variable factors as the monomeremployed, the duration of heating, the pressure employed and the type ofprocess, for example, continuous or batch. However, in general,

the catalysts of our invention can be used over a temperature range ofabout 30 C. to about 150 C. In a batch process, temperatures in therange of about 30 to about 70 C. will give satisfactory results, whiletemperatures within the range of about to about C. .are generallypreferred in .a continuous process. The pressure employed is alsosubject to wide variation and can be any of the conventional pressuresemployed in the polymerization of ethylenically unsaturatedpolymerizable compounds, although pressures in excess of about 10,000psi. are desirable, with pressures within the range of about 10,000p.s.i. to about 50,000 psi. being preferred, particularly with ethylene.The polymerization reaction is carried out in the presence of from fiveparts per million to 5% by weight of catalyst, based on the monomer tobe polymerized, with catalyst concentrations of 10 to 10,000 parts permillion being preferred in the case of ethylene. in addition, it is alsopossible to employ chain transfer agents, for example, hydrogen,aliphatic hydrocarbons .and the like or catalyst activators, forexample, sulfites, aromatic amines, sulfur dioxide, dimethyl aniline andthe like, in the process of this invention.

The novel catalysts of this invention are extremely versatile and can beemployed in the polymerization of any one or mixtures of ethylenicallyunsaturated polymeriza'ble compounds containing at least one CHFC groupand particularly those containing a CH :CH- group. These catalysts areparticularly suited to the polymerization of monoethylenicallyunsaturated compounds containing 2 to 10 carbon atoms or mixturesthereof. Suitable polymerizable compounds included within the scope ofthis invention, therefore, are compounds such as ethylene, propylene,butene, decene, styrene, acrylic acid, methyl acrylate, methylmethracrylate, vinyl chloride, vinylidene chloride, b-utadiene, isoprene.and the like.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention unless otherwisespecifically indicated:

EXAMPLE 1 As already indicated, the novel diacyl peroxides of thisinvention can be prepared by reacting the corresponding acyl halide withan inorganic peroxide at a relatively low temperature. To illustrate,0.02 mole of tetrahydrofuroyl chloride is stirred with 0.013 mole ofsodium peroxide in toluene at .a temperature of 1-5 C. for a period of6.5 hours. The excess sodium peroxide and the sodium salt oftetrahydrofuroic acid are filtered off. Thebis(tetrahydrofuroyl)peroxide can be isolated from solution in tolueneby pumping under vacuum.

EXAMPLE 2 As pointed out above, the tetrahydrofuroyl can also containalkyl substituents on the ring. Thus, using the same procedure as inExample 1, bis(5-tert.- butyl tetrahydro-Z-iuroyl)peroxide issynthesized by reacting 5-tert.- butyl tetrahydro-Z-furoyl chloride withsodium peroxide in toluene. The yield of bis(5-tert.-butyl tetrahydro-2-furoyl) peroxide is 37%.

EXAMPLE 3 The novel diacyl peroxides disclosed herein are extremelyeffective catalysts for the polymerization of ethylenically unsaturatedpolymerizable compounds, particularly ethylene, at low temperatures andhigh pressures. To illustrate this aspect of the invention several runsare carried out as follows:

A 100 cc. stainless steel autoclave, equipped with a magnetic agitator,is charged with peroxide catalyst in toluene solution. The autoclave isflushed with ethylene, then pressured to the desired level and thetemperature raised to reaction temperature. The reaction pressure ismaintained by addition of compressed gas for a period of two hours,after which time the reactor is cooled down and the unreacted ethylenevented. The polymer is recovered from the autoclave in the form of adry, spongy mass.

The results of these runs using the above procedure with the diacylperoxides of this invention and a prior art peroxide catalyst of similarstructure, i.e. bis-furoyl peroxide, are set forth in Table 2 whichfollows:

in reaction times involved, the catalysts of our invention, whenemployed in a continuous process, are used at temperatures up to about150 C. with excellent results.

Thus, this invention provides a novel class of diacyl 5 peroxidecompounds that can 'be used to catalyze the polymerization ofethylenically unsaturated polymerizable compounds at lower temperatures.These catalysts are particularly valuable in the high pressurepolymerization of ethylene to high density polymers. having increasedTable 2 Inherent Weight of Reaction Reaction Viscosity CatalystCatalyst, Tempera- Pressure, Yield, g Density (0.2% in Mg. ture, C.p.s.i. Tetralin (at 100 C.)

Bis(tetrahy lrofuroyl) peroxide 5 50 20, 000 6. 2 O. 951 1. 23 Do- 10 8020, 000 21. 2 0. 948 1. 19 Bis(5-tert.-butyl tetrahydro-2-furoyDperoxide 20 60 20, 000 6. 5 0. 949 1. 32 Bisfuroyl peroxide 5 5020, 000 less than .2

Upon examination of the above table it is readily apparent that thediacyl peroxides of this invention are extremely effective at lowtemperatures to form high density polymers, :whereas unsaturatedperoxides of similar structure, for example, lbisfuroyl peroxide areextremely ineffective.

EXAMPLE 4 As previously stated, the novel catalysts of our invention arevery versatile in that they can be used in the polymerization of any ofthe ethylenically unsaturated polymerizable compounds known in the artand particularly the monoethylenically unsaturated polymerizablecompounds containing 2 to 10 carbon atoms at low temperatures. Toillustrate this aspect of this invention,ibis(tetrahydrofuroyl)peroxi-de is employed to catalyze thepolymerization of methyl metha-crylate, styrene and vinyl acetate usingthe procedure which follows:

One tenth gram of the peroxide catalyst in toluene solution is placed ina vial and the toluene removed by pumping under vacuum. Twenty grams ofmonomer are charged and the vial sealed after flushing with nitrogen.The vials are heated for 4 hours at 60 C., cooled to room temperatureand opened. The yields of polymer and their inherent viscosities, asdetermined in .a 0.2% solution of tetralin at 100 C., are set forth inthe following table.

Table 3 Monomer Yield Inherent Viscosity Methyl methaorylate 12. 7 1. 32Styrene 14. 2 0. 45 Vinyl acetate.-- 15. 1 0.73

Due to the different half-life requirements of batch and continuousprocesses resulting fromthe difference where R is an alkyl group and nis an integer from 0 to 1, inclusive.

2. The compound of claim I where containing 1 to 10 carbon atoms.

3. The compound of claim 1 where n is 1.

4. Bis(tetrahydrofuroyl) peroxide.

R is an alkyl group 5. Bis(5-tert.-butyl tetrahydro-Z-furoyl)peroxide.

References Cited by the Examiner UNITED STATES PATENTS 2,957,030 10/60Bankert 260--610 2,610,965 9/52 Vandenberg 26080 2,813,127 11/57 White260-6l0 2,957,030 10/60 Bankert 260-610 NICHOLAS S. RIZZO, PrimaryExaminer.

JOSEPH L. SCHOFER, JOHN D. RANDOLPH,

Examiners.

1. A DIACYL PEROXIDE HAVING THE FORMULA: